1. Field of the Invention
The present invention relates to inter-vehicle communication methods and inter-vehicle communication devices, and more particularly, to an inter-vehicle communication method and an inter-vehicle communication device for performing communication by sequentially relaying transmission information among vehicles.
2. Description of the Related Art
Developments in communication technologies enable communication among moving objects, such as among vehicles, (referred to as inter-vehicle communication). For such inter-vehicle communication, a method for transmitting accident information to vehicles behind, one-by-one along the road when an accident occurs has been suggested. In such a method, however, only one-to-one communication is performed even if a plurality of vehicles exists in an area where data is relayed. Thus, the communication load increases, and hardly any other information can be transmitted.
Another method (first known art) has been suggested in which a transmission vehicle transmits (or broadcasts) information without specifying reception vehicles, the reception vehicles receive the information and appropriately display the information, and at the same time, broadcast the reception information to other vehicles, and such broadcasting (multi-hop) is sequentially repeated. According to the first known art, the communication area can be increased even for inter-vehicle communication with a limited communication distance.
Also, as a second known art, a method for preventing an increase in the bandwidth used for information transmission by deleting unnecessary data even if the number of relays (the number of hops) increases, in other words, even if the number of relaying communication devices increases, is disclosed in Japanese Unexamined Patent Application Publication No. 2002-135201.
In broadcast-type inter-vehicle communication according to the first known art, due to the relaying performed by all the vehicles for multi-hop, the traffic volume significantly increases. If the number of relay vehicles is reduced, communication reaches only a limited area.
In the second known art, although deletion of data prevents an increase in the bandwidth used for information transmission, the problem of the increase in the number of calls, in other words, the increase in the traffic volume, cannot be solved.